As social applications are widely applied, a proximity discovery function becomes increasingly important. For example, a user expects to know, in a timely manner, whether a friend appears around or leaves. The proximity discovery function makes people's life and work become more convenient. For example, after arriving at an office, a user can immediately know, by using the proximity discovery function, a colleague who is about to arrive at the office.
The proximity discovery function may be implemented by using a device to device (hereinafter referred to as D2D) communications technology. An existing D2D bearer establishment procedure is as follows: A source user equipment (hereinafter referred to as UE) initiates a D2D service to a target UE; a network carries, according to a service requirement, a D2D indication in a bearer establishment message that needs to be used to perform the D2D service, and sends the bearer establishment message to a base station; and the base station controls, according to the bearer establishment message from the network, a related UE to perform measurement and discover and establish a D2D link. If the D2D link cannot be established due to a cause such as insufficient resources or a long distance between the target UE and the source UE, the bearer establishment procedure fails, and the D2D service of the source UE cannot be established. The source UE may abandon the service or re-initiate a normal service request to the target UE.
For some services, a UE is more concerned about whether a service is established successfully rather than that D2D must be used for communication. In the prior art, because a D2D link cannot be established due to a cause such as insufficient resources and a long distance between a target UE and a source UE, a D2D service initiated by the source UE fails, and the source UE re-initiates a normal service request to the target UE. In this way, a service delay is large, which deteriorates service experience of a user, and causes more signaling overheads to an operator's network because a service is performed twice repeatedly.